At a Glance

Why Get Tested?

To help investigate unexplained flow of breast milk (galactorrhea), abnormal nipple discharge, absence of menstrual periods, and/or infertility in women; in men, to help diagnose the cause of decreased libido and/or erectile dysfunction; to detect and monitor a prolactin-producing pituitary tumor (prolactinoma)

When to Get Tested?

When you have symptoms of elevated prolactin, such as galactorrhea and/or visual disturbances and headaches; during a workup for infertility; for follow-up of low testosterone in men; periodically to monitor for recurrence of a prolactinoma

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

None; however, the sample should be collected 3 to 4 hours after waking.

The Test Sample

What is being tested?

Prolactin is a hormone produced by the anterior portion of the pituitary gland, a grape-sized organ found at the base of the brain. Normally present in low amounts in men and non-pregnant women, prolactin's primary role is to promote lactation (breast milk production). This test measures the amount of prolactin in the blood.

Prolactin secretion is regulated and inhibited by the brain chemical dopamine. The prolactin level is usually high throughout pregnancy and just after childbirth. During pregnancy, the hormones prolactin, estrogen, and progesterone stimulate breast milk development. Following childbirth, prolactin helps initiate and maintain the breast milk supply. If a woman does not breastfeed, her prolactin level soon drops back to pre-pregnancy levels. If she does nurse, suckling by the infant plays an important role in the release of prolactin. There is a feedback mechanism between how often the baby nurses and the amount of prolactin secreted by the pituitary as well as the amount of milk produced.

A common cause of an abnormally elevated prolactin level is a prolactinoma, a tumor of the pituitary gland that causes excess production of prolactin. Prolactinoma is the most common type of pituitary tumor and is usually benign. They develop more frequently in women but are also found in men. Problems resulting from them can arise both from the unintended effects of excess prolactin, such as milk production in a woman who is not pregnant or nursing and, rarely, in a man (galactorrhea) and from the size and location of the tumor.

If the anterior pituitary gland and/or the tumor enlarge significantly, it can put pressure on the optic nerve, causing headaches and visual disturbances, and it can interfere with the other hormones that the pituitary gland produces. In women, prolactinomas can cause infertility and irregularities in menstruation while in men, these tumors can cause a gradual loss in sexual function and libido. If left untreated, prolactinomas may eventually damage the surrounding tissues.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

The Test

How is it used?

Prolactin levels may be used for several reasons. Prolactin is a hormone produced by the pituitary gland and its primary role is to help initiate and maintain breast milk production in pregnant and nursing women.

Prolactin testing may be used, along with other hormone tests, to help:

Determine the cause of breast milk production not associated with pregnancy or breast-feeding (galactorrhea)

A man has symptoms such as decreased sex drive (libido), nipple discharge, or infertility or has a low testosterone level

When a person has a prolactinoma, prolactin levels may be ordered periodically to monitor the progress of the tumor and its response to treatment. They may also be ordered at regular intervals to monitor for prolactinoma recurrence.

What does the test result mean?

Men and non-pregnant women will normally have only small amounts of prolactin in their blood. Prolactin levels do, however, need to be evaluated based on the time of day that they are collected. The levels will vary over a 24-hour period, rising during sleep and peaking in the morning. Ideally, a person's blood sample should be drawn 3 to 4 hours after waking.

A high level of prolactin (hyperprolactinemia) is normal during pregnancy and after childbirth while the mother is nursing.

Is there anything else I should know?

Stress from illness, chest wall trauma, seizures, lung cancer, and use of marijuana can cause moderate increases in prolactin.

Drugs that can cause an elevated prolactin include estrogen, tricyclic antidepressants, risperidone, opiates, amphetamines, hypertension drugs (reserpine, verapamil, methyldopa) and some drugs that are used to treat gastroesophageal reflux (cimetidine). Nipple stimulation may cause a moderate increase in prolactin blood level.

Low prolactin levels may be caused by drugs such as dopamine, levodopa, and ergot alkaloid derivatives.

Prolactinomas are often small. Along with prolactin levels, a health practitioner may do an MRI (magnetic resonance imaging) of the brain to locate and determine the size of the tumor as well as the size of the pituitary gland.

Common Questions

1. What other tests may be done to evaluate an elevated prolactin?

Other tests that may be done include testosterone (levels will usually be low in a male when prolactin is high), FSH, and LH (to help evaluate ovulation and fertility), an MRI of the brain (to show pituitary enlargement and help locate a tumor), and an eye examination (to evaluate visual disturbances). Elevated prolactin levels require further laboratory tests to ensure that the elevation is not due to macroprolactin (see Question 4).

3. How are prolactinomas treated?

Prolactinomas may be treated with medications that act like dopamine (such as bromocriptine or cabergoline) to decrease prolactin production. Treatment can reduce prolactin levels and symptoms and restore fertility, but the medications may have to be taken for several months or years. Surgery is sometimes necessary if the prolactinomas are large or not responding to treatment. This surgery is delicate and requires an experienced surgeon. Sometimes, despite medication and/or surgery, the prolactinoma recurs.

4. What is macroprolactin?

A number of otherwise healthy people have elevated prolactin levels because some of the prolactin in their blood is in a different form called macroprolactin. Macroprolactin is prolactin that is bound to a protein (immunoglobulin), is not active in the body, and does not indicate the presence of disease. If an elevated prolactin is found, further laboratory tests may be done to make sure that this is not due to macroprolactin.

Article Sources

NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

(2009 May). Prolactinoma. National Endocrine and Metabolic Diseases Information Service [On-line information]. Available online at http://www.endocrine.niddk.nih.gov/pubs/prolact/prolact.htm through http://www.endocrine.niddk.nih.gov. Accessed April 2010.

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This article was last reviewed on May 15, 2014. | This article was last modified on December 19, 2014.

The review date indicates when the article was last reviewed from beginning to end to ensure that it reflects the most current science. A review may not require any modifications to the article, so the two dates may not always agree.

The modified date indicates that one or more changes were made to the article. Such changes may or may not result from a full review of the article, so the two dates may not always agree.